Abstract

An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar startospheric ozone depletion, is from the temperature fluctuations induced by mountain waves. However, this formation mechanism is usually missing in chemistry-climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate the representation of stratospheric mountain wave-induced temperature fluctuations by the UK Met Office Unified Model (UM) at high and low spatial resolution against Atmospheric Infrared Sounder satellite observations over the Antarctic Peninsula. At a high horizontal resolution (4 km) the mesoscale configuration of the UM correctly simulates the magnitude, timing, and location of the measured temperature fluctuations. By comparison, at a low horizontal resolution (2.5° × 3.75°) the climate configuration fails to resolve such disturbances. However, it is demonstrated that the temperature fluctuations computed by a mountain wave parameterisation scheme inserted into the climate configuration (which computes the temperature fluctuations due to unresolved mountain waves) are in excellent agreement with the mesoscale configuration responses. The parameterisation was subsequently used to compute the local mountain wave-induced cooling phases in the chemistry-climate configuration of the UM. This increased stratospheric cooling was passed to the PSC scheme of the chemistry-climate model, and caused a 30-50% increase in PSC surface area density over the Antarctic Peninsula compared to a 30-year control simulation.